The invention pertains to fluid delivery systems. More particularly, this invention relates to fluid flow and pressure regulation systems including valves, valve control systems, irrigation flush systems, pressure relief systems, and controlled fluid delivery nozzles.
Significant advances have recently been developed in the field of agricultural irrigation. More particularly, increases in water and energy costs coupled with an improved understanding of crop-water relations has led to an increase in demand for precision irrigation management techniques. Because of this demand for precision irrigation management techniques, there has been a movement to develop low volume-high frequency irrigation systems. For example, a drip irrigation system, also referred to as trickle irrigation, is one example of a low volume-high frequency irrigation system.
A drip irrigation system provides several advantages over other types of irrigation systems, such as flood irrigation systems, furrow irrigation systems, and many sprinkler-based irrigation systems. A well designed and properly maintained drip irrigation system can realize a very uniform fluid application over a field, with variations on the order of less than ten percent across the field. Accordingly, a grower can achieve greater control over the quantity of water delivered to a crop in the field in order to more precisely meet known water requirements for the crop, and to maintain a proper balance between soil moisture and aeration. Additionally, water-soluble fertilizers can be carefully metered, or xe2x80x9cspoon-fedxe2x80x9d to the crop using a drip irrigation system because the drip irrigation system can deliver fluids (and fertilizer) at precisely the rate and location required by the crop which corresponds to a growth stage of the crop. Even furthermore, careful metering of fluid including water, fertilizer, and pesticide can decrease disease and weed pressure on crops, as well as lower energy requirements and reduce environmental impact.
One form of drip irrigation system uses drip-tape. Drip tape is a thin-walled, polyethylene product that is usually buried at a nominal depth within a crop bed, for the case of row crops. Alternatively, the drip tape can be buried adjacent to a tree or vine row in orchards and vineyards. One distinguishing feature of drip tape is that drip tape employs a turbulent flow path between a main flow channel, or supply tube, and an emitter, or outlet. Such feature results in a consistent, definable relationship between discharge and pressure. However, drip tape is not pressure compensating. Therefore, great care and precision should be exercised in the design phase of an irrigation project in order to ensure that pressure variations do not exceed certain defined criteria.
As a result, to ensure such precision, fields are typically mapped using a survey grade global positioning system (GPS) in order to develop accurate topographic maps from which an irrigation system is then designed. As an example of the importance in developing an accurate topographic map, a design error of 1 psi will result from having an elevation error of 2.3 feet, which could lead to a 10% error in flow. Such errors may become compounded when integrated over large areas of a field. The operating pressure within drip tape is limited to a narrow range, which rarely exceeds 12 psi, and is seldom lower than 4 psi. It follows that the lower the operating pressure the more important the accuracy of design calculations. Accordingly, such a design error will have a significant effect on the operating pressure within a drip tape.
For most regions where crops are grown and irrigated, crops are rotated from field to field in order to break cycles of plant diseases, and to maintain soil tilth and fertility. Because of the need to rotate crops, many growers who wish to use drip irrigation systems need to implement portable or xe2x80x9ctemporaryxe2x80x9d drip irrigation systems that can be moved from field to field. Typically, these systems consist of above-ground components that can be re-used each year, as well as adapted to changes in irrigation system design. However, drip tape from such systems is discarded each year. Furthermore, design changes are usually necessary to accommodate changes in topography, water supply and field size. In contrast to the disposable drip tape, portable and reusable components from such systems include sand media filters for water treatment, PVC fittings, control valves, control wire and xe2x80x9clay-flatxe2x80x9d tubing.
Pressure control is principally achieved within a field using control valves. As a control element, control valves regulate pressure by controlling the flow rate into or out of a portion of the delivery system where regulation is required. A xe2x80x9cmainxe2x80x9d control valve is typically located near the water supply and regulates downstream pressure of the flow to the main line. The main control valve also serves the purpose of sustaining a minimum pressure on the upstream side to properly operate the filtration equipment. A xe2x80x9czonexe2x80x9d control valve provides secondary control and allows for the precise regulation of pressure at a xe2x80x9czonexe2x80x9d. A xe2x80x9czone xe2x80x9d is understood to refer to an irrigated block within the field, and thereby being supplied by a single distribution line or sub-main line within a multiple zone irrigation system. Operation of the irrigation system is typically automatic and is accomplished through a centralized programmable controller for zone valve operation. Zone control valves, in this application, regulate pressure from a range of 17 to 30 psi, on the supply side, down to a zone pressure of approximately 11.5 to 13.0 psi, depending on the design requirements.
One exemplary control valve is the Nelson 800 Series control valve sold by Nelson Irrigation Corporation, of Walla Walla, Wash. Such control valve employs a control volume and an expandable and retractable xe2x80x9csleevexe2x80x9d or xe2x80x9cbootxe2x80x9d diaphragm, positioned and seated within the valve body about the main flow path. The sleeve acts as a throttling element as the control volume is allowed to expand or retract, modulating flow through the valve. Such control valves are known as self-directing control valves, where the force necessary to position the throttling element is derived from the fluid being regulated. The Nelson 800 Series control valve is unique in its design in that it employs internal struts to maintain the sleeve in good throttling position, even at low flows. This is known as proportional throttling. The flow path through the valve keeps streamlines relatively uniform and parallel, minimizing friction loss due to turbulence. Due to the low overall operating pressures of drip irrigation systems, minimizing friction loss is important. Competitive valves, employing alternative throttling methods, create greater turbulence and friction loss and do not provide the same flow control. The loss coefficient depends primarily on the shape of the valve, which determines the degree of flow separation and generation of additional turbulence. Filling and draining of the control volume is governed by a mechanical pressure regulating pilot.
Mechanical pilots are typical to self-directing pressure regulating valves in agricultural irrigation. In order to reduce flow through the valve and therefore lower downstream pressure, pressurized water from upstream of the valve is allowed to pass to the control volume through the pilot. Conversely, in order to increase the downstream flow and raise downstream pressure, water from the control volume is allowed to vent to atmosphere back through the pilot. A set point, or regulated downstream pressure, is determined by a reference load. A spring within the mechanical pilot provides the reference load, and fluid pressure, both upstream and downstream, is in hydraulic communication with the mechanical pilot in a scheme known as xe2x80x9cthree-way logicxe2x80x9d. The sensitivity of the pilot is determined largely by the spring constant and by the size of the orifice regulating fluid flow into the pilot body. In operation, the balance of force between the spring reference load and the diaphragm determines the position of the pilot shaft and, therefore, which ports will open. Such control valves represent the current state of the art in agricultural irrigation, and work relatively well for most applications where precise pressure regulation is not a requirement.
However, with the classical mechanical pilot, there are a number of potential sources where accuracy and precision may be lost. First, inertia can cause a resistance to movement of the structural element that is responsible for directing fluid into and out of a control volume sleeve for a mechanical pilot system. Secondly, hysteresis of the mechanical portions of a mechanical pilot creates different operating points, depending on the direction of approach. Thirdly, mechanical fatigue of the spring within the mechanical pilot can be responsible for varying the reference load. Finally, temperature effects on the spring within the mechanical pilot can be responsible for varying the reference load. It is understood that the third and fourth cases can lead to a change in the relationship between an applied force, such as compression of the spring, and a change in length of the spring. This relationship is mathematically modeled and referred to as Hook""s Law. Such inherent limitations cause pressure set points to vary throughout the irrigation season by as much as 2 or 3 psi.
Lay-flat tubing comprises an above-ground conduit by which water is transmitted from a pump and sand media filter to drip tape. Lay-flat tubing is relatively easy to install, retrieve, store and transport, making it one preferred method of distributing water within a field. Lay-flat tubing is typically constructed of 3-ply polyester yarns that are sandwiched between a vinyl tube and a cover. The yarns, tube and cover are simultaneously extruded together, forming the lay-flat tubing.
One problem with lay-flat tubing results because lay-flat tubing is not completely rigid and, therefore, it expands and contracts in response to pressure changes within a transmission line. In response to such expansion and contraction due to pressure changes, lay-flat tubing stores and releases energy. Such response can result in transmission of pressure waves throughout the distribution lines of an irrigation system, causing control valves to react accordingly, and in turn causing line pressure to continuously cycle up and down. Pressure waves within an irrigation system are initiated by sudden changes in flow velocity, usually caused by the reaction of a control valve. These conditions can be exacerbated by the presence of entrapped air. Typical pressure oscillations can have a period ranging from 3-4 seconds to a minute or more. This situation prevents the irrigation system from reaching a xe2x80x9csteady-state xe2x80x9d condition. However, it is important to reach a steady-state condition in order to realize uniform fluid flow to various portions within a field, as the field is being irrigated and, possibly, fertilized.
Additionally, for irrigation systems of sufficient size and scale, phenomenon such as dead time and lag time become important issues. Dead time is a delay in response due to the time it takes for fluid to flow from one point to another. Lag time is a period of time over which a response occurs and is additive to the dead time. For the mechanical pilot, when a corrective action occurs at the control valve, dead time and lag time can lead to over-corrective changes in the control volume and, therefore, the position of the throttling element. The mechanical pilot is susceptible to this as the control volume is in continuous hydraulic communication with a source of flow (typically upstream) during the corrective action.
Accordingly, field scale irrigation systems are largely designed using steady-state flow theory. Moreover, pressure settings for control elements within a given system design have been calculated using steady-state theory based on a particular design flow. However, as discussed above, irrigation systems may include non-rigid, or elastic, components, such as lay-flat tubing, and such steady-state conditions may be difficult, if not impossible, to realize. More particularly, the interaction and reaction of control valves in response to pressure waves propagating through the main line and sub-main portions, or lines, of an irrigation system prevents the prompt realization of a steady-state system. Such oscillation prevents control valves within an irrigation system from settling down to a steady-state flow and pressure regime. A normal, steady fluid flow regime is generally necessary in order to realize a proper distribution of moisture to crops in a field.
Hence, pressure control for most agricultural irrigation systems has traditionally been realized using such a mechanical pilot and control valve. Pressure control has been attempted for both downstream pressure regulation as well as for upstream pressure sustaining.
In industries outside of agricultural irrigation, such as in manufacturing or water-works, where fluid pressure regulation is often required, advances have been made in the area of feedback control to improve the performance of pressure regulating control valves. Specifically, the pressure of the fluid being regulated is continuously monitored and deviations from the set point cause a controller to re-position the throttling element to attain the proper fluid pressure. In feedback control theory, one method, commonly known as PID control, causes the corrective signal to be a function of the measured error. This method has been successfully applied to numerous process control loops including pressure regulation. However, numerous factors prohibit the adoption of these commercially available systems within agricultural irrigation and, specifically, drip irrigation. The most important factor is cost, as it is necessary for the agricultural producer to minimize production costs to be profitable. Therefore, the cost must be competitive with existing irrigation technology. Secondly, the flow control at low pressures and pressure loss characteristics desired are generally not present with valve technology from the aforementioned industries. Thirdly, the size, weight and physical dimensions of valve technology from these industries also make it impractical for many agricultural applications. Moreover, it is desirable that the technology be compatible with existing irrigation controllers, consuming minimal power. Lastly, it is desirable that intelligent control features be available to recognize unsteady flow conditions, such as pressure oscillations within the irrigation system, and to take corrective action.
Accordingly, improvements are needed in the way fluid is delivered and fluid pressure is controlled, particularly where an irrigation system includes non-rigid or elastic components.
An electronic control system and valve are provided for use with irrigation systems that have elastic components or have sufficient length that fluid compressibility introduces elasticity into an irrigation system as well as in the case where there is entrapped air and/or significant elevation changes in the irrigation system. Control of fluid pressure and steady state flow have previously been difficult to realize for such systems.
According to one aspect, a fluid delivery and control system is provided for a fluid delivery line having elastic components. The system includes a pressure sensor, an electronically controlled valve, processing circuitry, and computer program code logic. The pressure sensor is operative to detect fluid pressure within a fluid delivery line. The electronically controlled valve includes an adjustable flow regulating aperture disposed in the line, interposed along a linear flow axis, and operative to regulate fluid flow through the line. The processing circuitry communicates with the pressure sensor and the electronically controlled valve. The computer program code logic is executed by the processing circuitry and is configured to generate an output signal. The output signal comprises an operating parameter of at least one of the pressure sensor and the electronically controlled valve to adjust flow capacity of the flow regulating aperture of the valve to dissipate pressure oscillations within the fluid delivery line.
According to another aspect, a fluid flow control system is provided, including a pressure sensor, an electronically controlled flow regulating valve, and a processor. The pressure sensor detects fluid pressure within a fluid delivery line. The electronically controlled flow regulating valve is provided in the line to impart a substantially linear flow axis and is operative to regulate fluid flow through the line. The processor communicates with the pressure sensor and the electronically controlled flow regulating valve, with the sensor generating a PID feedback control signal. The processor is operative to regulate fluid flow through the valve to dampen out pressure oscillations in the line.
According to yet another aspect, a fluid flow control system is provided, including a pressure sensor, a primary control valve, an auxiliary fluid delivery line, an auxiliary control valve, and a processor. The pressure sensor is configured to detect fluid pressure within a primary fluid delivery line. The primary control valve is provided in the primary fluid delivery line and is operative to regulate fluid flow through the primary fluid delivery line. The auxiliary fluid delivery line extends between the primary control valve and the fluid delivery line. The auxiliary fluid delivery line is operative to deliver fluid between the primary control valve and the fluid delivery line to controllably adjust a throttling element of the primary control valve. The auxiliary control valve is provided in the auxiliary fluid delivery line and is operative to regulate fluid flow through the auxiliary secondary primary fluid delivery line. The processor communicates with the pressure sensor and the auxiliary control valve. The processor is operative to controllably adjust the throttling element of the primary control valve by regulating operation of the auxiliary control valve to deliver fluid between the primary control valve and the fluid delivery line via the auxiliary fluid delivery line.
According to yet even another aspect, a method is provided for controlling pressure oscillations within fluid of a fluid delivery line. The method includes: providing an electronically controlled valve disposed within a fluid delivery line and a pressure sensor communicating with the fluid delivery line; detecting fluid pressure within the fluid delivery line using the pressure sensor; and controllably regulating the electronic valve in response to the detected fluid pressure to regulate fluid flow through the line; wherein controllably regulating the electronic valve comprises controllably generating an output signal including an operating parameter of at least one of the pressure sensor and the electronic valve to regulate operation of the valve so as to dissipate pressure oscillations within the fluid delivery line.